Record numbers of Venezuelan migrants have been crossing into the United States in recent months, posing a new border challenge for the Biden administration and raising concerns that more of the nearly 6 million people displaced from the South American nation could be heading north.

U.S. authorities intercepted 13,406 Venezuelan migrants along the Mexico border in October, the highest one-month total ever and more than double the number taken into custody in August. The influx includes Venezuelans who left their homes years ago for Colombia and other countries in the region, as well as more recent emigrants fleeing violence, economic collapse and authoritarian rule.

The U.S. government does not recognize Venezuelan leader Nicolás Maduro as the country’s legitimate president, limiting the ability of U.S. Immigration and Customs Enforcement to send migrants back.

As a result, nearly all of the Venezuelans crossing the Mexican border are being released into the United States. ICE carried out just 150 deportations to Venezuela between October 2020 and August 2021, a period when nearly 40,000 Venezuelans crossed the U.S. border illegally, according to agency statistics.

Those figures contrast with the treatment of Haitian migrants, whom the Biden administration has expelled en masse since September using the Title 42 emergency public health law. Last month fewer than 1 percent of Venezuelans were expelled under Title 42, while 48 percent of Haitians were returned.

“This is a hard one for the administration,” said Andrew Selee, president of the nonpartisan Migration Policy Institute in Washington. “They don’t want to send people back to Venezuela. At same time, if Venezuelan nationals are allowed in, it creates incentives for others to try.”